Tread Softly, My Heart — Stella Ross

When her twin sister, Jenny, disappears, Laurel leaves her partner in charge of their fashion store while she goes to Germany in search of her. On the plane, a young man makes a nuisance of himself. He turns up a second time when Laurel takes a bus ride to the clinic where her sister once worked.

Threatened by a stranger, she is forced to leave Cologne in disguise. Yet again, she bumps into good-looking Paul Troughton and a chain of unusual events occurs.

After she is forced to share a room with him beside Lake Constance, she realizes she is in love with him. But, on finding her sister, it seems that what he has felt for Laurel all along has been only infatuation.